1. Field of the Invention
This invention relates to an improved environment system for sealed hard disk assemblies, and more particularly to a system that extends the operating life of the hard disk assemblies when subject to high operating temperatures.
2. Description of the Prior Art
FIG. 1 schematically illustrates a commercially available sealed, hard disk drive and its environment control enclosure that makes the disk drive suitable for use in rugged applications where it is subject to high temperature and mechanical shock and/or vibration. One such sealed hard disk and environment control enclosure is available from Miltope Corporation and referred to by Miltope as the LPC Series of rugged high capacity, low profile, shock and vibration resistant disk drives employing sealed, disk drive housings. These products are ruggedized for operation in severe field environment where extremes of temperature, shock, vibration, humidity and air pressure are common. They are designed for xe2x80x9con-the-movexe2x80x9d operation in tracked and wheeled vehicles, as well as airborne and shipboard applications. As illustrated in FIG. 1, this prior art disk drive includes a commercially available sealed hard disk drive 10, such as the sealed hard disk drive available from Toshiba, IBM Corp., Seagate and others. Such hard disk drives include a disk housing 12, which is sealed except for a very small opening 14 that allows a small amount of gas sealed in the housing 12 to egress and ingress during disk start up and shut down respectively. A hard disk 16 within the housing 12 rides on a spindle 17 driven by a motor 18, both of which are also located within the housing 12. A flying head 20 is servo positioned over a desired track on the disk 16 in order to read from and write data onto the disk. The housing 12 is supported in a sealed, ruggedized hard disk drive housing 22 by resilient mounts 24, i.e. devices to mechanically isolate rapid acceleration due to shock or vibration, for example, of the hard disk drive housing 22 from the disk housing 12. The hard disk drive housing 22 is an air tight aluminum housing filled with an inert gas or, if desired, with dry or low humidity air. This sealed aluminum housing 22 can also house a control electronics module 30. An embedded closed loop servo system compensates for temperature variation, ensuring reliable head positioning. An air tight connector 32 provides a signal and power interface between the components inside the hard disk drive housing 22 and connections (not shown) outside of the housing. As will be appreciated by those skilled in the art, hard disk drives of the type shown schematically in FIG. 1, store multi-gigabytes of data on a 2.5 inch or 3.5 inch disk, with the hard disk drive housing 22 having a foot print of approximately 5 inches by 8 inches by 1.5 inches deep for a 3.5 inch disk, or appropriately smaller for a 2.5 inch or smaller hard drive. The expected mean time between failures is normally in excess of 100,000 hours in a normal environment application.
While quite satisfactory in normal office type operation, the hard disk drive systems of the type shown in FIG. 1 have experienced a significant increase in failures when operating at very high temperatures.
An object of this invention is the provision of a hard disk drive system with a small footprint and rugged shock resistance (i.e. of the type described in connection with FIG. 1) but which can operate in a high temperature and/or high humidity environment without a significant decrease in mean time between failure.
Applicant has identified the cause of an increase in failure rate of hard disk systems operating in high temperature environments as the lubricant used to lubricate the disk drive motor 18. Oil from the spindle motor has been found to wick and/or vaporize out of the motor bearing when operated at high temperatures. The lubricant has been found to form a deposit on the flying head and disk surface, eventually causing it to contact the disk and cause permanent damage as well as cause spindle motor bearing failure which causes permanent damage. In addition, when the hard drive is turned on, internal air is expelled as the air is heated through the breathing hole/filter generally used in disk drives of the magnetic media type due to the high speed rotation of the disk platter. When a drive is powered off, and cools down, make-up air is drawn in. If humidity is present, the make-up air can contain humidity or other contaminants which can deposit residue on the read/write head and disk platters, which can cause unstable flying of the read/write head and cause damage to the unit which can result in permanent failure. In addition, the disk drive electronics have caused circuit drifts and failures at temperatures above 135xc2x0 F.
Applicant""s solution to the problem that applicant has identified is to provide an active heat transfer device inside an environmental housing in which the hard disk drive housing is placed, in order to transfer heat away from the hard disk drive without necessarily increasing the overall footprint of the system or coupling shock or vibration from the environmental housing to the disk drive. In some embodiments of the invention, the active heat transfer device is a thermoelectric solid state heat pump that uses the Peltier effect to move heat. As will be appreciated by those skilled in the art, such solid state heat pumps are commercially available, for example from Melcor corporation. These heat pumps consist of a number of p type and n type pairs connected electrically in series and sandwiched between two ceramic plates. When the heat pumps are connected to a d.c. source, current causes heat in each heat pump to move from one plate to the other, making one ceramic plate a relatively hot plate and the other ceramic plate a relatively cool plate, and creating a relatively hot side and a relatively cool side on the heat pump. In one embodiment of the invention, the environmental housing comprises an outer shell of a heat conductive material, such as aluminum, and a receptacle for receiving a hermetically sealed hard disk drive housing or cartridge. The receptacle comprises two side walls and a bottom wall, all made of heat insulating material, such as polyurethane, and a top wall comprising a heat conducting structure of a heat conducting material, such as aluminum. The heat pump is interposed between the heat conducting structure and the outer shell of the environmental housing, with the cool side of the heat pump contacting the heat conducting structure of the receptacle, and the hot side of the heat pump contacting the outer shell of the environmental housing. Fins of heat conducting material, such as aluminum, are positioned on the outside of the environmental housing. The heat insulation minimizes the transfer of heat from a hot environment to the disk drive, and heat in the disk drive is transferred to the environment by the active heat transfer device and the environmental housing, including the fins.
An arrangement is provided for biasing the hard disk drive housing into heat conducting contact with the heat conducting structure of the environmental housing.
In one embodiment, the biasing arrangement comprises wedge members interposed between the disk drive housing and the environmental housing, the wedge members cooperating with one another to bias the disk drive housing into heat conducting contact with the heat conducting structure of the environmental housing. The wedge members are associated with actuating mechanisms having portions which block the environmental housing door from closing when the disk drive housing is not in flat, heat conducting contact with the heat conducting structure and which permit the door to close when the disk drive housing is in flat, heat conducting contact with the heat conducting structure. Portions of the actuating mechanisms use the environmental housing as a fulcrum to eject a portion of the disk drive housing from the environmental housing.
In another embodiment, a wedge structure comprising a groove is defined in each side wall of the receptacle, each groove having a lower surface inclined upwardly from an end opening of the receptacle to the interior of the receptacle. A pin is provided on each opposed side of the hard disk drive housing, each pin being supported by the lower surface of a respective one of the grooves. As a result, as the hard disk drive housing is inserted into the receptacle, the leading end of the top surface of the housing is cammed into with the heat conducting structure at the top of the receptacle. The environmental housing has a door from which a wedge structure projects toward the disk drive housing. As the door is closed, the wedge structure biases the disk drive housing forward and upward into firm flat heat conducting contact with the heat conducting structure of the environmental housing. Thus, heat is transferred from the hard disk drive housing to the heat conducting structure of the receptacle, from the heat conducting structure to the heat pump, and from the heat pump to the shell and cooling fins of the environmental housing.
A plurality, e.g., two or three, of the solid state heat pumps are connected in parallel in thermal management circuitry which is a closed loop system used to provide the desired cooling for the disk drive. Each heat pump is operated significantly below its heat transfer capacity in order to significantly increase the efficiency with which the cooling is accomplished. The use of a plurality of heat pumps also provides redundancy in case one or more of the heat pumps should fail. If one of the pumps fails, the thermal management circuitry seeks to maintain a certain temperature differential or to not allow the drive temperature to exceed 55xc2x0 C. (internal) and therefore increased power proportionately. At below freezing, the direction of current through the solid state heat pump is reversed. As a result, heat is driven into the disk drive housing, thereby heating the housing. The exact temperature varies, depending on the type of disk drive and the spindle motor bearing friction. The friction varies according to the type of lubricating grease or oil used or, in the case of a non-lubricant bearing, the temperature at which the direction of current is reversed could be based on the friction at low temperatures. A temperature sensor, for example, a thermistor, is bonded directly to the metal hard disk drive for monitoring the temperature inside the disk drive housing.
In another embodiment, the heat pump is omitted in favor of a heat pipe. Heat pipes have been used to cool aircraft power supplies and densely packed electronics in portable computers. One particular type of heat pipe, manufactured by Thermacore, Inc. of Lancaster, Pa., consists primarily of a porous material soaked in a low vapor-point liquid, such as acetone or methanol. When the liquid is heated, it vaporizes and is forced to the center of the pipe. It then travels to one end, where it condenses and releases its heat. At that point, the cooled liquid is wicked back to where it started, and the process repeats. The heat pipe can be generally U-shaped, with one side being secured to the heat conducting structure of the receptacle, and the other side being secured to the outer shell of the environmental housing. Flexibility is provided in the heat pipe by, for example, a flexible bellows between the two sides of the heat pipe. Heat from the side in contact with the heat conducting structure flows through the heat pipe to the side in contact with the environmental housing.